Learn to Manage Chilling or Freezing of Farm Produce

Refrigeration, and the technology behind
it, is one of the most important aspects in the food supply chain and paramount
in getting food from the farm to the consumer in a fresh, edible and safe
state. Not only food, but cut flowers, seeds, extracted oils and other chemicals produced by farms all need to be kept at an optimum temperature; hence an understanding of refrigeration may be very important to farmers, traders and manufacturers of most types of farm produce.

When food is chilled it has an
advantageous effect on quality because transport of moisture is minimised
through refrigeration – it also extends shelf-life.When food is frozen it adds another
dimension – most bacteria don’t survive temperatures below -12°C and low
temperatures also slow the rate of both chemical and enzymic
change in foods. Freezing foods promptly after harvest extends shelf-life
by preventing deterioration, retains the texture, flavour colour and vitamin C
content. This also means that products that are seasonal are available to the
consumer all year round and lessens food wastage.

Lesson Structure

There are 8 lessons in this course:

Nature and Scope of Refrigeration

The Refrigeration Process

The Vapour Compression System

Heat Load Calculations

The Refrigeration Cycle: Refrigerants and Components

Applied Refrigeration: Farm Produce

Applied Refrigeration: Other Products

Freezing Goods

Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.

Aims

Explain the nature and scope of refrigeration by providing a general overview of the concepts.

Outline what happens to the physical properties of substances during refrigeration and different refrigeration methods, especially vapour compression.

Describe the vapour compression refrigeration system and its components.

Describe the nature of cooling and freezing items and outline how to calculate the heat load to be removed in order to carry out these processes.

Outline the principles behind the basic refrigeration cycle, and selection of refrigerants and components.

Explain refrigeration and chilling techniques for a range of edible products.

Explain refrigeration and chilling techniques for a range of products other than edible produce.

Outline the difference between freezing and refrigerating and how freezing methods can be used to store a range of goods.

What things are refrigerated and what should not be?

The majority of items belonging to the overall categories of fruit, vegetables, meat, fish, cut produce and flowers can all be refrigerated, however not all items should be refrigerated. Refrigerating certain foods can actually change their flavour and not in a good way. It can even reduce their nutritional quality of accelerate the spoiling/decaying process.

The following are items that should generally not be chilled:

Bread: it is fine to freeze bread, but chilling bread causes it to dry out.

Herbs: chilling herbs can cause them to wilt faster.

Potatoes: storing loose potatoes in a fridge can adversely affect their flavour. If they are going to be stored in a fridge, then either store them loose or in a paper bag as a plastic bag can promote moisture and speed up the decaying process.

Fruits: some fruits can lose their flavours and textures if stored in fridges.

Generally, if unsure, consult the food preservation label that you will generally find on the items.

REFRIGERATION METHODS

As seen in the brief history of refrigeration, there are a number of natural and mechanical methods available which are all used in today’s society.

Ice Refrigeration

In this method, ordinary ice is used for keeping the space at a temperature below the surrounding temperature. The temperature of ice is generally 0oC and therefore can be used to maintain temperature of about 5-10oC. To use ice as a refrigeration method, a closed and insulated chamber is required. On one side of the chamber ice is kept whilst on the other side there is a space which is to be cooled or where the items to be cooled are placed. If a temperature below 0oC is required, then an ice/salt mixture can be used which lowers the freezing temperature of the ice mixture.

Dry Ice Refrigeration

Dry ice is solid carbon dioxide. It has a temperature of -78oC. Dry ice converts directly from a solid state to a gaseous state in a process called sublimation. Dry ice can be formed into various different shapes of blocks so that it can be packed in with frozen food that has to be kept frozen for long periods of time. When the dry ice gets converted to the gaseous state, it produces a refrigeration effect keeping the product frozen.

Mechanical Refrigeration

Mechanical refrigeration consists of a variety of methods, the Vapour Compression cycle, the absorption cycle, the adsorption cycle, the gas cycle and many others. What distinguishes these from the natural methods is that some form of mechanical input is required to drive the process and the processes are cyclical meaning that they do not require topping up as the natural methods would. These methods can be used over a variety of temperature ranges from high temperatures to cryogenic temperatures and the method chosen will be dependent upon the application required.

WHY STUDY THIS COURSE?

To understand the physics and engineering that makes refrigeration work.

When you understand how temperature is physically manipulated, you then have the basis for maintaining and managing refrigeration equipment.

Learn to choose what equipment you need to do the job at hand.

Learn how to chill, refrigerate or freeze different types of farm produce.

Be more capable as a farmer, produce processor, manufacturer or marketer of agricultural products.

As a farmer, value add to your products to increase cash flow.

Teach, Consult, Write better, as an agricultural or production horticulture expert.

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